1. Field of the Invention
The present invention relates to a semiconductor structure having controllable spatial distributions of dopant impurity atoms and to a process for producing the semiconductor structure. The structure is further characterized by enabling controlled electrical activation of a portion of the dopant atoms present in the semiconductor.
2. Description of Related Art
In integrated circuit manufacture, efforts are constantly being directed towards development of smaller sized semiconductor components. An important limitation on the size of each component or each element of such component is the thickness of various doped regions, such as n- and p-type layers. For example, it is becoming more and more critical to control dopant distribution and activation in polysilicon gates as the thicknesses of polysilicon gates are reduced.
In order to provide semiconductor components for various applications, dopant atoms implanted into a semiconductor substrate must be activated for carrying out electrical operations in the component. Typically, dopant atoms are diffused within the semiconductor and activated by annealing at elevated temperatures for long periods of time. These high temperatures and long annealing times often result in the thickening of doped layers or lateral diffusion of dopant species. In some cases the net result is expansion of the doped area into undesired regions. In extreme situations the high temperature and long annealing times can lead to electrical shorting of regions which are intended to be electrically isolated from one another. As a result, it has been difficult to obtain the desired distribution of dopant atoms while at the same time electrically activating selected dopant regions.
Some measure of control of the spatial distribution and electrical activation of dopants in single crystal silicon has been reported. For example, the effect of implanted argon atoms upon boron distribution and activation has been described in the references, A. Milgram and M. Delfino, "Effect of Argon Implantation on the Activation of Boron Implanted in Silicon", Appl. Phys. Lett. 42, 878 (1983), and M. Delfino, A. Milgram, and M. D. Strathman, "Epitaxial Regrowth of Silicon Implanted with Argon and Boron", Appl. Phys. Lett. 44, 594 (1984), both of which are incorporated herein by reference.
The effect of argon and other noble gas dopants upon boron diffusion in single crystal silicon has also been modeled mathematically in the reference, Sheldon Aronowitz, "Quantum Chemical Modeling of Boron and Noble Gas Dopants in Silicon", J. Appl. Phys. 54, 3930 (1983), which is incorporated herein by reference.
The effect of interactions among various p- and n-type dopants in single crystal silicon has been described in the reference, S. Aronowitz, "Interaction Between Interstitial Atoms in Silicon: Arsenic-Argon-Boron and Boron-Argon-Phosphorus", J. Appl. Phys. 63., 1037 (1988), which is incorporated herein by reference.
The effect of germanium implantation upon dopant diffusion in single crystal silicon has been described in the references, Sheldon Aronowitz, "Dopant Diffusion Control in Silicon Using Germanium", J. Appl. Phys. 68, 3293 (1990) and S. Aronowitz, C. Hart, S. Myers, and P. Hale, "P-Type Dopant Diffusion Control in Silicon Using Germanium", J. Electrochem. Soc. 138, 1802 (1991), both of which are incorporated herein by reference.
Polysilicon, unlike single crystal silicon, is characterized by having numerous grain boundaries between crystals. Dopant diffusion along grain boundaries is a common occurrence and may lead to deactivation of dopant species. Thus, the control of dopant distribution and activation in polysilicon presents problems not encountered in single crystal silicon. Previously it has not been possible to control dopant distribution and activation in polysilicon.
Accordingly, it is a principal object of the present invention to provide a method of controlling dopant distribution and activation in polysilicon.
Another object of the present invention is to provide semiconductor structures in which dopant distribution in polysilicon layers is predetermined.
Another object of this invention is to provide a simple and convenient method for controlling the distribution and activation of dopant species in polysilicon by the implantation of electrically neutral atomic species.
Other objects and advantages of the present invention will become apparent in the course of the following detailed description and disclosure.